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Enter two positive ratio parts and the new amount you want the first part to become. Press Calculate to see the simplified ratio, the scale factor, and the corresponding second part; decimal parts are scaled to whole numbers before they are reduced.
Equivalent ratios preserve the same relationship between quantities. Divide the new first part by the original first part to get the scale factor, then multiply the second part by that factor. For the simplified ratio, divide both parts by their greatest common factor; decimal parts are first scaled to whole numbers (1.5 : 2.5 becomes 15 : 25, then 3 : 5) when up to six decimal places can make them whole, and are otherwise shown exactly as typed.
A recipe uses flour and sugar in a 2:3 ratio. Enter 2, 3, and a new first part of 10. The scale factor is 10 ÷ 2 = 5, so the new ratio is 10:15.
Enter 12, 18, and a new first part of 8. Divide the original parts by 6 to get 2:3; the scale factor from the original ratio is 8 ÷ 12 = 2/3, so the second part becomes 12.
Just enter the decimals: 1.5 : 2.5 is scaled to 15 : 25 and reduced to 3 : 5 automatically. This works for parts with up to six decimal places; a pair that never becomes whole numbers, such as 1/3 : 2/3, is shown as typed rather than rounded into a ratio that no longer matches your inputs.
Yes. A flour-to-sugar ratio of 2:3 is different from 3:2. Match the first field and the new first part to the same quantity.
This tool requires both parts and the new first part to be above zero. It is intended for positive quantities such as ingredients and scale lengths, not signed ratios.
Add the ratio parts first. For a total of 50 split 2:3, one share is 50 ÷ 5 = 10, giving 20 and 30. This tool scales from a known first part; it does not have a total-sharing mode.
Ratios connect to percentages and unit conversions, but each answers a different question. Use the related calculators for those tasks and read the ratios lesson for sharing and proportion problems. Related tools: Percentage Calculator, Unit Converter. Read the Ratios & Proportions lesson or practice ratios & proportions to build confidence without relying on a calculator.